BINDING OF SOLUTE ATOMS TO I) ISLO ('ATIONS 89 of solute. The atmosphere inhibits the motion of dislocations, and therefore it influences the response of the material to mechanical stress. Cottrell and Nabarro assume that the interaction causing the solute atom atmosphere to form is characterized by an interaction energy which is elastic in origin and arises because of the effective size difference between solute and solvent atoms in solution, in addition, they propose that the density of the solute atmosphere is related to the interaction energy by a Boltzmann-type distribution function. Since the appearance of the aforementioned papers, however, it has been realized that these ideas present an oversimplified picture of the solute atom-dislocation interaction. Indeed, the interaction is composed of several contributions in addition to the elastic misfit interaction, and furthermore, the Boltzmann function only can describe the concentration profile of the solute atom cloud under limited experimental conditions.

The purpose of the present article is to provide a current and unified digest of the prevalent ideas concerning solute atom-dislocation interactions. In addition, the article indicates the limitations of binding energy theory which arise because of the necessary simplifying assumptions. The following section treats, from a thermodynamic point of view, the principles that govern the segregation of solute atoms to dislocations, and provides a foundation from which various solute atom-dislocation interactions can be analyzed. The specific interactions are considered in Section 3, and recent experiments which yield a quantitative measure of the interactions are discussed in Section 4. Section 5 summarizes the salient results reviewed in this article.